He is arguably the greatest match-point player tennis has ever seen yet misses the type of shot you would never see him missing. Well now we have.
It just shows you how sport is fascinating and random. I remember reading an article a few weeks ago about how sport is very random. This is very true. There are some things in life and sport that cannot be explained.
Djokovic failing to convert match point is just another example of that. Did he choke? I don't think so, but who knows? It was perhaps a lack of concentration. But again, who knows?
There is no rational explanation for it. We try to analyse and pontificate, and get the 'whys' out there, but sometimes it just happens for no particular reason.
Wawrinka earned his win today. He should have enjoyed more success. He gets a reputation for not being very strong which is clearly not true.
He is mentally very strong. Why did he beat Djokovic this time a year after losing to him at the Australian Open a year ago? I don't know. Only he would be able to tell you the reasons why it happened.
Why was Djokovic not able to produce his best tennis when he always does? Perhaps there is a risk that it will eventually go against you if you keep being pushed to the limits.
His failure to convert that high volley was astonishing. Perhaps the decision to serve and volley was the wrong play.
But Boris Becker being his new coach had no effect. He wouldn't have coached him to miss that shot. It is bizarre.
Wawrinka has probably lost matches he felt he should have won. Now Djokovic must contemplate such a feeling.
Tomas Berdych and Wawrinka will fancy their chances of reaching the final, but I think we can safely assume the winner will come from the other half of the draw.
But at least he does not need to confront the champion Djokovic if and when he gets there.
Federer is looking sprightlier than he has been in some time, and his back seems to be pain-free. He seems to be particularly sharp at net working with Stefan Edberg.
Murray will like playing Federer.
I don't think those two are soulmates. And I think Murray enjoys playing him.
I thought Murray would win this tournament before it started, but it is not such a one-sided contest as I expected before the tournament.
If it gets tough against Roger, I'd narrowly back Andy to win.
I didn't think Federer was a contender at the start, but now that has changed. It looks to be a very tight contest with Andy just slightly having the edge.
Murray won't be running scared of Nadal if he gets through.
Federer used to have his number, but that all changed when Murray beat him last year in the semi-finals.
I think Rafa is beatable. Murray could certainly beat him. I'm not sure about Roger.
I think Andy and Roger could be a five-set contest, but it will be a major sign of Murray's form if he can perform well in the last eight.
Andy has been in three finals in Australia and could well be in a fourth this year which would be an amazing achievement.